*If you do not have access to the Apache configuration file
then the code above will also work if included in your .htaccess
file.

Then I tuned on the Apache module mod_expires:

LoadModule expires_module modules/mod_expires.so

And that fixed it good. :-)

The configuration above forces image files to persist in the browser’s cache
for 30 days (2592000 seconds). These are probably not ideal settings so someone might
want to improve this. I’m no server expert so I copied the expiration settings
of the W3C’s site.